Polystable semiconductor device



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HAROLD L.ARMSTRONG ATTORNEY United States Patent Office 3,2061; 11Patented Sept. 14, 1965 3,206,611 POLYSTABLE SEMICQNDUCTOR DEVIQE HaroldL. Armstrong, Euclid, Ohio, assignor to Clevite Corporation, Cleveland,Ohio, a corporation of Ohio Original application Jan. 19, 1954, Ser. No.404,851, now

Patent No. 2,927,221, dated Mar. 1, 1969. Divided and this applicationJuly 9, 1959, Ser. No. 830,973

7 Claims. (Cl. 307--88.5)

This invention relates to a semiconductor device for use in variouselectrical circuits and is a division of Patent No. 2,927,221, filedJanuary 19, 1954, entitled Semiconductor Devices and Trigger CircuitsTherefor in the name of H. L Armstrong.

In its broad general aspect the present invention is concerned with theprovision in various electrical devices of a novel semiconductorconfiguration in which a pair of base electrodes have ohmic contacts toopposite ends of a semiconductor for establishing an electric fieldtherein, and a plurality of other electrodes have rectifying junctioncontacts to the semiconductor at locations thereon which are normally atthe same potential, intermediate the respective potentials at the baseelectrodes. In the absence of a change in the potential gradient betweenthe ends of the semiconductor, no current flows between any of thejunction and base electrodes through the semiconductor. However, whenthe potential gradient in the semiconductor between a predetermined oneof the junction electrodes and one of the base electrodes is altered,current is caused to flow between that junction electrode and thecorresponding base electrode through the semiconductor, current at theother junction electrode or electrodes being cut off at this time. Thiscondition remains stable until the potential relations between theconducting junction electrode and the semiconductor change so thatcurrent at this electrode is cut off and current flows at one of thepreviously non-conducting junction electrodes, and so on, in acontrolled sequence.

The foregoing generic principles of the present invention may beemployed advantageously in a variety of semiconductor configurationswhich may be used in various practical circuits including, but notlimited to, bistable and polysta-ble circuits, square wave generators,wave squarers, and ring counters.

Accordingly, it is an object of the present invention to provide a novelsemiconductor device adapted for use in a variety of electricalapparatus.

Another object of the present invention is to provide a novel bistablecircuit employing a semiconductor device.

A further object is to provide a semiconductor device and associatedcircuitry which is stable in any one of several current conductingconditions in the semiconductor,

Still another object of this invention is to provide a novel ringcounter which employs a semiconductor.

These and other objects and advantages of the present invention will beapparent from the following description of several preferred embodimentsthereof, which are shown in the accompanying drawings to illustrate theprinciples of the present invention without intending, however, thatthis invention be considered as being limited to these specificembodiments.

In the drawings:

FIGURE 1 is a perspective view of one embodiment of the presentinvention, including a semiconductor together with a schematic diagramof a circuit providing bistable operation;

FIGURES 2-5 are schematic views showing the current and voltageconditions in the FIGURE 1 semiconductor device in successive stages ofits operation;

FIGURE 6 is a schematic view of another embodiment of a semiconductordevice and associated circuitry according to the present invention whichis adapted for current conducting operation successively in any ofseveral stages;

FIGURES 7 and 8 illustrate the current and voltage conditions in theFIGURE 6 device in successive stages of its operation; and

FIGURE 9 shows a ring counter which constitutes a still furtherembodiment of the present invention.

Referring to the drawings, in FIGURE 1 there is shown an embodiment ofthe invention, which may be used for bistable circuit operation. In thisembodiment there is provided an intrinsic semiconductor in the form of athin, relatively wide, rectangular bar of purified germanium. A baseelectrode [2 has ohmic contact with one end of the semiconductor and ismaintained at a positive potential +V as by battery B At the other endof semiconductor 80, the base electrode b has ohmic contact, thiselectrode being at a negative potential V applied by battery B On oneface of the semiconductor, midway between its ends, a pair of spacedindium dots 81 and 82 are fused into the germanium to provide rectifyingP junctions thereat, denoted P and P in FIG. 1. One the opposite face ofthe semiconductor, a relatively large mass 83, of lead-antimony alloy isfused into the germanium to provide a rectifying N junction thereat. TheN junction is located on this face of the semiconductor midway betweenthe base electrodes b and b and has its opposite ends disposed directlyopposite the P and P junctions, respectively.

In the FIG. 1 circuit, the P junction is connected to a parallelcombination of condenser 84 and resistor 85, Which have their oppositeterminals grounded. In like manner, the P junction is connected to aparallel combination of condenser 86 and resistor 87, which have theiropposite terminals grounded. The N junction is connected through acoupling condenser 38 to a source of negative input voltage appliedbetween terminals 91a and Mb. A resistor 89, is connected between apositive voltage +V (provided by battery B and the N junction, so thatnormally the N junction is biased positive with respect to ground andpositive with respect to the contiguous portion of the semiconductor,

Theoretically, if the FIG. 1 device were perfectly balanced, none of theP and N junctions would draw current in the absence of an input signal.However, this theoretical condition will not hold true in practice andby suitable design one or the other of the P junctions can be caused tostart drawing current in the absence of an input signal. Assuming (FIG.2.) that the P junction starts conducting first, the hole currentemitted into the semiconductor by P will be swept toward the negativebase electrode 12 This lowers the resistivity of the semiconductor underthe P junction and distorts the potential gradient in the semiconductorso that the zero equipotential 90 will assume the position shown in FIG.2. The P junction, grounded at this time, will have a potential negativewith respect to the contiguous semiconductor material and therefore willbe cut off.

When a negative input signal is applied at terminals 91a, 91]), the Njunction will go negative with respect to the contiguous semiconductormaterial and will inject electrons into the semiconductor Theseelectrons will flow up to the positive base electrode 1),, distortingthe potential gradient in the semiconductor so that the zeroequipotential 90 will assume the location shown in FIG. 3, between thejunctions and the negative base electrode b The semiconductor contiguousto both P junctions will have a potential negative with respect to both,and both P and P will be cut off.

At the end of the negative input signal, the zero equipotential willtend to move away from the negative base electrode [7 At this time the Pjunction is still at ground potential, while the P junction is slightlynegative with respect to ground because in its previous conducting stateit had rendered the upper terminal of condenser 84 negative with respectto ground, which condition cannot change instantaneously. Therefore, theother P junction, P being at a higher potential will begin to drawcurrent first. The N junction ceases to draw current due to its positivebias from +V The holes injected by P into the semiconductor will beswept toward the negative base electrode 12 distorting the potentialgradient in the semiconductor so that the zero equipotential 90 willassume the position shown in FIG. 4. P remains cut off.

The next negative input signal to terminals 91a and 91b drives the Njunction negative with respect to the contiguous semiconductor material,cutting off both P junctions (-FIG. 5) as before.

At the completion of this negative input pulse, the P junction will drawcurrent and the P junction remains out off. Thus, bistable circuitoperation is obtained in which the P junctions conduct in alternatesequence.

A further embodiment of the present invention is shown in FIGS. 68. Inthis embodiment there is provided a slab 10d of N-type germanium whichhas a lateral dimension appreciably greater than its length. Positiveand negative base electrodes [2 and b have ohmic contacts with oppositeends of the germanium slab, extending completely thereacross. Thepositive base electrode 12 is connected through resistor 107 to asource, battery 13,, of positive potential ,+V while the negative baseelectrode b has a connection through a resistor 138 to a source, battery3:, of negative potential V,. Midway between the base electrodes thereare provided a series of P junctions, ia, 11 ic za 213 P Sa: 31 P30: inthe form of evenly spaced indium dots fused into the face of germaniumsemiconductor. The P junctions P P P are connected to ground throughresistors 112, 101, and 102, respectively. The P junctions P P P areconnected in parallel with each other and through a common resistor 103to a common input terminal 1045a. The junctions P P and P are biasednegative with respect to ground through a resistor 105' connected to asource, battery B of negative voltage V The other P junctions P P and Pare connected in parallel with each other and through :a common resistor104 to a common input terminal 110a. The junctions P P and P are biasednegative with respect to ground through a common resistor 109 connectedto a source, battery B of negative voltage V The resistors 107 and 108are of equal value, so that the zero equipotential in the semiconductorwould extend through the portions of the semiconductor contiguous to theP junctions in the absence of current to any of the P junctions.

In the operation of this device, let it be assumed that initiallyjunction P is drawing current. The holes injected by junction P into thesemiconductor 100 are swept to the negative base electrode [7 resultingin current through, and a voltage drop across, resistor 108.Accordingly, b will assume a negative potential lower in magnitude thanthe positive potential at b causing the zero equipotential in thesemiconductor to assume a position below the P junctions, exceptadjacent the conducting junction P This condition is indicated in FIG.7, wherein reference numeral 111 denotes the zero equipotential line.This condition, in which P draws current, is stable. Thus, at this time,the portion of the semiconductor contiguous to junction P is negativewith respect to this junction, while the semiconductor contiguous toeach of the other P junctions has a potential positive with respect toeach of those junctions. Because of the potential distortion due to thehole current injected into the semiconductor 100 by junction P at thistime, the semiconductor contiguous to the adjacent junction P will beless positive than at locations contiguous to the other non-conducting Pjunctions.

When a positive input signal is applied between input terminals 106a and106b, P will be driven positive with respect to the semiconductormaterial contiguous to it. However, the other junctions P and P to whichthis same input pulse is applied will not be driven positive withrespect to the contiguous semiconductor portions because of the morepositive potential of these semiconductor portions than in thesemiconductor at P these portions of the semiconductor not having beenaffected as much by the hole current injected into the semiconductor bythe remote junction P Also, when junction P begins to conduct it causesa voltage drop across resistor 108 which causes the potential in thesemiconductor underlying the junctions P and P to remain positive. Also,when P conducts there is a resulting voltage drop across resistor 103 inthe input circuit for junctions P P and P so that none of thesejunctions goes very far positive. Therefore, the combined effect is thatthe junctions P and P are not driven positive with respect to theunderlying semiconductor portions, and neither of these junctionsconducts. Consequently, junction P only will draw current when thisinput pulse is received.

The holes injected by junction P into the semiconductor will be swept tothe negative base electrode b resulting in a voltage drop acrossresistor 108 which maintains base electrode b at a negative potential ofa magnitude less than the postive potential at base electrode b since atthis time conducts much more current than 12 Accordingly, the zeroequipotential 111 will assume a position closer to the negative baseelectrode 12 than to the positive base electrode b except at theconducting junction P This condition is indicated in FIG. 8.

This condition is unstable, lasting only as long as there is asufficiently positive input signal across input terminals 106a and10612. When this input signal is removed, the negative bias V drives Pnegative with respect to the contiguous portion of the semiconductor,cutting off P At the same time, the negative base electrode [5 tends toassume the potential V which is more negative than while P wasconducting. Therefore, the entire zero equipotential 111 tends to shiftupward toward the positive base electrode b But at this time, because ofthe hole current just previously injected into the semiconductor byjunction P the semiconductor contiguous to the adjacent junctions P andP will be somewhat less positive than at the other nonconductingjunctions. Therefore, by applying a properly timed positive signalacross input terminals 110a and 11%, current may be switched to the nextjunction P In effect, the hump in the zero equipotential line 111 shiftsover to P before the zero equipotential has had a chance to level off asa result of the current cut off at P When this positive input signal isapplied, junction P is driven positive with respect to the underlyingportion of the semiconductor and will, therefore, draw current,injecting holes into the semiconductor. The other P junctions P and Pconnected to input terminal 110a will not be driven positive withrespect to the underlying portions of the semiconductor when thispositive input signal is received across input terminals 110a, 11Gbbecause these underlying portions of the semiconductor had been slightlymore positive, while junction P was drawing current, than was theportion of the semiconductor contiguous to the adjacent junction P Inaddition, the voltage drops across resistors 104 and 107 resulting fromthe current to P maintain the junctions P and P negative with respect tothe underlying semiconductor portions, so that neither of thesejunctions conducts at this time.

With junction P drawing current, the holes injected by P into thesemiconductor are swept to the negative base 3 electrode b resulting ina voltage drop across resistor 108. Accordingly, the negative baseelectrode 11 is at a negative potential of less magnitude than thepositive potential at the positive base electrode b Accordingly, thezero equipotential 111 will assume a position closer to the negativebase electrode b than to the positive base electrode b except at theconducting junction P This condition is unstable, lasting only as longas a sufficiently positive input signal exists across input terminals110a, 1101).

When the positive input ignal at terminals 110a, 1101) is terminated,junction P cuts off due to the negative bias from B; through resistor109. At the same time, due to the current cut off, the negative baseelectrode b tends to assume the more negative potential V which in turntends to shift the zero equipotential 111 toward the positive baseelectrode b When this happens, the hump in the Zero equipotential shiftsover to the adjacent grounded junction P While junction P had beenconducting, junction P was at ground potential while the other junctionP adjacent to the conducting junction (P was at a potential negativewith respect to ground. Due to the distortion of the potentialdistribution through the semiconductor which resulted from the holecurrent injected by junction P the potential in the semiconductorcontiguous to each of the adjacent junctions P and P as less positivethan at the other non-conducting junctions. Therefore, the hump in thezero equipotential will shift to the more positive of these adjacentjunctions, which in this case is the grounded junction P Therefore, Pbegins to draw current when the positive input signal at P isterminated.

The sequence of the foregoing cycle may be repeated so that thejunctions P P P P and P conduct successively in that order.

FIGURE 9 illustrates a still further embodiment of the present inventionintended for use as a ring counter. In this embodiment the semiconductoris in the form of a flat annular disk 120 of N type germanium. Apositive base electrode b has ohmic contact with germanium disk entirelyaround its outer periphery and is biased from a source, battery B ofpositive potential +V through resistor 124. The negative base electrodeb has ohmic contact at the inner periphery of the annular germanium disk120 and is biased from a source, battery B of negative potential -Vthrough resistor 125. Midway between the positive and negative baseelectrodes, there are provided a series of indium dots P P P P P P P P PP P and P arranged in circular fashion and fused into one face of thesemiconductor. indium dots provide evenly spaced P junctions on thesemiconductor midway between the positive and negative base electrodes.The junctions P P P and P are connected to ground through resistors 121,122, 123, and 119, respectively. The junctions P P P3,, and P areconnected in parallel with each other and through a common resistor 126to a common input terminal 129a. Each of these junction P P is normallybiased negative from a source, battery B of negative voltage at apotential V through resistor 130. The other P junctions, P P P and P areconnected in parallel with each other and through a common resistor 127to a common input terminal 135a. Through a resistor 136 each of thejunctions P P is biased source, battery B of negative from a negativevoltage at a potential V In the operation of this device, assuming thatjunction P is drawing current initially, the hole current injected by Pinto the semiconductor 120 will be swept toward the negative baseelectrode b Due to this hole current, the potential gradient through thesemiconductor between the base electrodes will be distorted so that thezero equipotential will extend between junction P and the positive baseelectrode 12 and between each of the non-conducting electrodes P P etc.,and the negative base electrode These 12 Therefore, at each of thesenon-conducting junctions the germanium will be at a potential positivewith respect to each non-conducting junction. However, the germaniumunderlying the junctions P and P which are adjacent the conductingjunction P will be less positive than at the other non-conductingjunctions due to the effect of the hole current injected into thesemiconductor by the conducting junction P If, next, a positive inputsignal is applied between input terminals 129a, 1291), it will drivejunction P positive with respect to the underlying germanium. Thisjunction will begin to draw current, emitting hole current into thesemiconductor which is swept toward the negative base electrode b Thisdistorts the potential gradient in the semiconductor so that the hump inthe zero equipotential shifts to junction P The previously conductingjunction P is cut off and the other junctions remain nonconducting. Thispositive input signal at terminals 129a, 1291) does not drive either ofthe junctions P P and P positive with respect to the underlyinggermanium because those portions of the semiconductor had been morepositive while junction P was conducting than was the germaniumunderlying junction P Also, as in the embodiment of FIGS. 68, thevoltage drop across resistors 126 and due to the current to P maintainthe portions of the semiconductor underlying junctions P P and Pnegative with respect to these junctions. Junction P continues to drawcurrent only as long as there is a positive input signal at terminals129a, 1291].

By substantially immediately applying a positive input signal to theinput terminals a, 1351; the next junction, P in the series may berendered conductive in like manner as just described, cutting off all ofthe other junctions.

Then, after the positive input signal across terminals 135a, 13% isremoved, the grounded junction P would conduct next.

The foregoing sequence may be repeated indefinitely to render the otherjunctions P P conductive in succession, providing a ring counter typedevice quite similar in operation to the device of FIG. 68, described indetail above.

From the foregoing description, it will be evident that the presentinvention is susceptible of numerous and varied embodiments, which areadapted for various particular applications. However, while in theforegoing description and the accompanying drawings there have beendisclosed several specific preferred embodiments of the presentinvention, it is to be understood that various modifications, omissionsand refinements which depart from the specific disclosed embodiments maybe adopted without departing from the spirit and scope of thisinvention.

I claim:

1. A semiconductor device comprising a semiconductor, means forestablishing a potential gradient through the semiconductor, anelectrode having a first rectifying junction of one conductivity type onone face of the semiconductor, and a pair of electrodes having spacedrectifying junctions of the same conductivity type as each other anddifferent from that of said first rectifying junction on the oppositeface of the semiconductor, the semiconductor contiguous to saidrectifying junctions being at equal potentials in the absence of currentto one of said rectifying junctions.

2. A semiconductor device comprising a semiconductor, an electrodehaving a first rectifying junction of one conductivity type to one faceof the semiconductor intermediate its ends, a pair of electrodes havingspace-d rectifying junctions of the same conductivity type as eachother, and different from that of said first rectifying junction, to theopposite face of the semiconductor intermediate its ends, and a pair ofbase electrodes having ohmic contacts to opposite ends of thesemiconductor and biased differently to establish a potential gradientthrough the semiconductor with the portions of the semiconductorcontiguous to the rectifying junctions being at equal potentials in theabsence of current to any of the rectifying junctions.

3. A semiconductor device comprising a body of semiconductor material ofone conductivity type having spaced faces, means for establishing apotential gnadient parallel to said faces in said semiconductor, and aplurality of electrodes having rectifying junctions of a differentconductivity type to one face of the semiconduct-or at locations thereonwhich are simultaneously at equal potentials in the absence of currentto any of the rectifying junctions, and means for rendering saidrectifying junction-s conductive individually in succession.

4. A ring counter comprising a semiconductor of one conductivity typehaving spaced faces, base electrodes 'having ohmic connections to spacedportions of the semiconductor and biased differently to establish apotential gradient parallel to said faces in the semi-conductor, aplurality of electrodes having rectifying junctions of a ditferentconductivity type on the semiconductor, said rectifying junctions beingarranged in an annular series on the face of the semiconductor betweensaid 'base electrodes at locations on the semiconductor which aresimultaneously at equal potentials intermediate those of the baseelectrodes in the absence of current to any of the rectifying junctions,and means for rendering said rectifying junctions conductiveindividually in succession.

5. A semiconductor device comprising a semiconductor of oneconductivity-type, base electrode having ohmic connections to thesemiconductor at spaced 10- cations thereon for establishing an electricfield therein, a .plurality of electrodes having rectifying junctions ofthe same conductivity-type as each other and different from theconductivity-type of the semiconductor to one face of the semiconductorbetween the base electrodes at locations which are simultaneously at thesame potential intermediate the potentials at the base electrodes in theabsence of current between any of the rectifying 8 junction electrodesand the semiconductor, and means for rendering said rectifying junctionsconductive individually in succession.

6. A semiconductor device comprising a quadrangular plate ofsemiconductor material of one conductivity-type, a respective baseelectrode making ohmic contact with said semiconductor on each of onepair of opposite edges thereof, a plurality of electrodes havingrectifying junctions of the same conductvity-type as each other anddifferent from the conductivity-type of said semiconductor disposed onthe face of said semiconductor plate at equally spaced locations along aline substantially parallel to and midway between said base electrodes,and means for rendering said rectifying junctions conductiveindividually in succession.

7. A semiconductor device comprising an annular semiconductor of oneconductivity-type, respective base electrodes making ohmic contact withsaid semiconductor along the inner and outer circumferences thereof, aplurality of electrodes having the same conductivity-type as each otherand different from the conductivity type of said semiconductor formingrectifying junctions therewith, said junctions being arranged to form anannulus concentric with and spaced radially midway between said baseelectrodes, and means for rendering said rectifying junctions conductiveindividually in succession.

References Cited by the Examiner UNITED STATES PATENTS 2,655,607 10/53Reeves 307-885 2,851,615 9/58 Sziklai et al. 30788.5 2,889,469 6/59Green 307-885 JOHN W. HUCKERT, Primary Examiner.

HERMAN K. SAALBACH, GEORGE N. WESTBY,

ARTHUR GAUSS, Examiners.

1. A SEMICONDUCTOR DEVICE COMPRISING A SEMICONDUCTOR, MEANS FORESTABLISHING A POTENTIAL GRADIENT THROUGH THE SEMICONDUCTOR, ANELECTRODE HAVING A FIRST RECTIFYING JUNCTION OF ONE CONDUCTIVITY TYPE ONONE FACE OF THE SEMICONDUCTOR, AND A PAIR OF ELECTRODES HAVING SPACEDRECTIFYING JUNCTIONS OF THE SAME CONDUCTIVITY TYPE AS EACH OTHER ANDDIFFERENT FROM THAT OF SAID FIRST RECTIFYING JUNCTION ON THE OPPOSITEFACE OF THE SEMICONDUCTOR, THE SEMICONDUCTOR CONTIGUOUS TO SAIDRECTIFYING JUNCTIONS BEING AT EQUAL POTENTIALS IN THE ABSENCE OF CURRENTTO ONE OF SAID RECTIFYING JUNCTIONS.